Well, every time you think about past events or study some history, it in a sence takes you back through time, of course only in your mind and not physically(Yea this is nothing new dont mean to sound sarcastic im really not trying to be)As far as with acctually bending and manupulating the fabrics of time to be able to control time would indeed be quiet a accomplishment but theres some things in life we will never know at least not in our life span-Heres a question to go along with yours~ If time travel was possible some day are you sure the future would want the past it visits to know they were from the future so in a sence you really cant prove they have come but maybe you also couldnt prove they have not

Mariko has a point; there would be a huge risk of changing the future and not always for the better. For example, it would be great if we could use the information we have about Hitler's whereabouts during the Second World War so we could go back, hunt hinm down and kill him. However, we have no idea what that would do to the future and what effects it would have. It seems like a good idea, but everything happens for a reason. We don't always have to like the reason.

Attempting to return to the past involves some seriously theoretical physics. Especially since the universe exsists in 11 dimensions and we humans operate in a 4 dimensional place in it; x, y, z, and t. That would be four different types of equations alone before you could even consider combining them to possibly come up with a theory.

it would be great if we could use the information we have about Hitler's whereabouts during the Second World War so we could go back, hunt hinm down and kill him. However, we have no idea what that would do to the future and what effects it would have.

I read somewhere (and don't know it it's true) that Churchill had an opportunity to have Hitler assassinated and decided against it. The fear was that another believer in the cause, who would be a more effective leader, might take his place and win the war.

it would be great if we could use the information we have about Hitler's whereabouts during the Second World War so we could go back, hunt hinm down and kill him. However, we have no idea what that would do to the future and what effects it would have.

In Michio Kaku's book, Hyperspace, Kaku explains how changing the past, according to relativity, is not possible.

Relativity gives us a simple method to sort through the thorniest of these paradoxes. We will make use of the "world line" method, pioneered by Einstein.

...Our world line never really begins or ends. Even when we die, the world lines of the molecules in our bodies keep going. These molecules may disperse into the air or soil, but they will trace out their own never-ending world lines. Similarly, when we are born, the world lines of the molecules coming from our mother coalesce into a baby. At no point do world lines break off or appear from nothing.

...Our world line thus contains the entire body of information concerning our history. Everything that has ever happened to us--from our first bicycle, to our first date, to our first job--is recorded in our world line...

...With the aid of the world line, we can now picture what happens when we go back in time. Let's say we enter a time machine and meet our mother before we are born. Unfortunately, she falls in love with us and jilts our father. Do we really disappear, as depicted in Back to the Future? On a world line, we now see why this is impossible. When we disappear, our world line disappears. However, according to Einstein, world lines cannot be cut. Thus, altering the past is not possible in relativity.

The second paradox, involving re-creating the past, poses interesting problems, however. For example, by going back in time, we are fulfilling the past, not destroying it. Thus the world line of the inventor of time travel is a closed loop. His world line fulfills, rather than changes, the past.

...Thus perhaps we can fulfill the past, but never alter it. World lines, as we have stressed, cannot be cut and cannot end. They can perform loops in time, but never alter it.

This would mean that if you happened to go back in time with advanced technologies and the whereabouts of Hitler during WWII, you would not be able to alter the events in history, only fulfill known history. According to this conjecture, despite your greatest efforts to rid history of Hitler's wrath, you would not succeed and Hitler would live. Perhaps something happens to thwart your plans.

Even so, you should also keep in mind that although relativity is mostly universally accurate in accordance with nature, it's still incomplete. The yet to come Theory of Everything (Grand Unified Field Theory) would provide a much better view as to whether or not time travel is even possible and what happens when you travel.

Hmm, that's interesting I have not heard that. Even if you couldn't erase world lines just fulfill them, you might end up altering the future without knowing it. You wouldn't be erasing would lines just changing small parts. I find it rather hard to wrap my mind around not being able to change the past. According to relativity that is. If you were to go back and dilberatly do some things that you had not done, it would change the future because every action has different consequences.

At any rate, the TOE will be able to give some more conclusive insight into the matter of time travel once it has been solved. Similar to the relativity point of view, quantum mechanics has another view on the issue:

In the quantum theory, we can have multiple states of any object. For example, an electron can exist simultaneously in different orbits (a fact which is responsible for giving us the laws of chemistry). Similarly, Schrodinger's famous cat can exist simultaneously in two possible states: dead and alive. So by going back in time and altering the past, we merely create a parallel universe. So we are changing someone ELSE's past by saving, say, Abraham Lincoln from being assassinated at the Ford Theater, but our Lincoln is still dead. In this way, the river of time forks into two separate rivers.

Meshing together the quantum standpoint of time travel (that parallel worlds result from inacting superpositions when changing the past) and the relativity standpoint of time travel (that the past cannot be changed or altered but only fulfilled) will undoubtedly give a better depiction of time travel and what it entails once both views have been successfully fused together.

"The Physics of Time Travel"
http://www.mkaku.org/articles/phys_time_travel.shtml [Broken]